Alot is 21 ft by 30 ft. to support a fence, an architect wants an upright post at each corner and an upright post every 3 ft in between. how many of these posts are needed?

What we know:
Lot= 21 x 30ft
Perimeter=2l+2w
Want to put 4 corner post and one post every 3 ft

What we need to find:
How many post we need.

Perimeter=2 (21)+2 (30)=42+60=102ft

102/3=34

34 posts are needed.